【作者】 程世庆；

【导师】 岑可法； 骆仲泱； 倪明江；

【作者基本信息】 浙江大学 ， 工程热物理， 2003， 博士

【摘要】 目前我国环境污染依然严重，主要污染物排放总量仍处于较高水平。我国大气污染以煤烟型大气污染为主，其主要污染物为烟尘和SO₂，大气中SO₂的87％来自于煤的燃烧。流化床燃烧脱硫技术是一种经济有效的清洁的燃烧技术，石灰石、白云石和消石灰等钙基脱硫剂来源广、原料易得、价格低廉，是国内外最常用的燃烧脱硫剂。贝壳的主要成分是碳酸钙，与石灰石有相似的化学成分。本文通过大量的试验研究和理论分析，研究贝壳和石灰石等钙剂脱硫剂在各种条件下的脱硫反应性能，研究贝壳和石灰石微孔结构的差别，以及微孔结构对脱硫性能的影响。 利用热重分析技术对27种贝壳和18种石灰石在常压、大气气氛下的煅烧反应和模拟烟气中的硫化反应进行了试验研究，研究了颗粒粒径、炉膛温度、SO₂浓度、O₂浓度等对脱硫剂钙利用率的影响，对不同种类脱硫剂的脱硫性能进行了评价。研究结果表明，贝壳中富含一些Na₂O、K₂O等碱金属盐类物质，多数贝壳的脱硫效果优于石灰石，且其最佳脱硫温度比石灰石高大约50～150℃。硫化反应对SO₂浓度的反应级数在1～1.6之间，最终脱硫效率和钙转化率随SO₂浓度的升高而增大。硫化反应速率和钙转化率随氧浓度增加而增加，但当氧浓度超过4.85％后，钙转化率反而下降。 建立了流化床燃烧脱硫试验台，对5种贝壳和1种石灰石在流化床条件下的脱硫性能进行了研究。结果表明，贝壳的脱硫效率远大于石灰石，而且在某一温度段脱硫效率随温度升高而上升，其最佳脱硫温度比在热重条件下略低。贝壳和石灰石的脱硫效率η随钙硫比的增加而增大，贝壳在钙硫比为2.5时，脱硫效率趋于稳定，而石灰石在钙硫比达到3时脱硫效率才趋于稳定。 利用扫描电镜和压汞仪对贝壳和石灰石的微观结构进行了测试。与石灰石相比，各种贝壳原始结构中含有一些大孔，其比表面积和比孔容较大。贝壳煅烧后孔径较大，主要孔径分布范围为0.2～5μm，石灰石煅烧后比表面积虽然很大，但其孔径和比孔容比贝壳的小的多，主要孔径范围在0.005～0.1μm之间。在贝壳中，比表面积较大的贝壳钙的转化率较高，因而脱硫剂合理的孔径分布应该大于0.2μm，但上限应尽量减小。随煅烧温度的增加，原始孔径较大的贝壳，孔径减少，比表面积增加，脱硫反应增强；而孔径本来较小的石灰石，最可几孔径增加，比表面积减少，反应速度更低。在孔隙分布研究的基础上，研究了脱硫剂孔隙的分形特性。各种贝壳煅烧后孔的分形维数较大，而石灰石煅烧后孔的分形维数较小。对同种脱硫剂分形维数最小时对应最佳脱硫温度，对于不同脱硫剂，分形维数较大时最佳脱硫温度也高。 在对前人提出的硫化反应模型基础上，对模型中涉及到的化学反应过程、扩散过程进行了探讨，建立了一个描述大孔脱硫剂脱硫反应的颗粒——分布孔模型，并对该模型进行了验证。该模型的理论预测值与实验值基本吻合，可以用来预测脱硫剂的钙转化率， 浙江大学博士学位论文程世庆，2003，6为实际应用提供理论指导。 研究了各种添加剂成分及其含量对贝壳和石灰石脱硫性能的影响。很多添加剂能够促进钙基脱硫剂的脱硫性能，而且存在一个最佳的添加量，添加剂的加入对脱硫剂内部微观结构的改善是影响脱硫效果的一个重要原因。 在实际循环流化床锅炉中进行了石灰石燃烧脱硫试验。研究了煤种、C留S比、粒径、床温等对循环流化床锅炉脱硫效率的影响，并对飞灰、循环灰中的钙转化率进行了分析。循环流化床锅炉中石灰石脱硫的最佳床温在900℃左右，最佳脱硫剂颗粒直径在0.2^1之间。挥发分含量较低的煤种，床层温度高，脱硫效率较低，灰分较高的煤，循环倍率低，脱硫效率下降。循环流化床锅炉中飞灰与循环灰中的钙是脱硫的主体，灰分较大的褐煤，飞灰中小颗粒的钙转化率最高，而灰分较低的贫煤，粒径在0.05⁰.075^之间的飞灰颗粒中钙转化率最大。更多还原

【Abstract】 In China, the environmental pollution is serious, and the emission quantity of major pollutant is now still very high. The flue gas from coal combustion is the main origin of air pollution, and the major pollutants are soot and sulfur dioxide (SO_<sub>2). About 87% SO₂ in air conies from coal combustion, especially from the coal-fired power plants. The fluidized bed combustion and desulphurization is the effective and economical clean coal technique, and the absorbents such as limestone, dolomite or lime are very ubiquitous and cheap, so they are widely used in the desulphurization of fluidized bed all over the world. The seashells are like limestone in the contents, their major content is calcium carbonate (CaCO₃). The aim of this paper is go deep into studying the desulphurization of calcium-based absorbent like limestone and shell at various conditions, and the difference of various absorbent at microstructure as well as its influence on the desulphurization through experiments and theoretical analysis.In this paper, 27 kinds of sea shells and 18 kinds of limestone were selected as sulfur absorbent; the calcinations and desulphurization of every absorbent were studied using thermal-gravimetric analysis （TGA） method at atmospheric or simulate flue gas respectively. The effects of absorbent type, particle diameter, furnace temperature and concentration of SO₂ as well as O₂ on the calcium sulphation ratio were investigated. As results, the desulphurization of most shells are excellent than that of limestone as their content of alkali metals such as sodium oxide (Na₂O) kalium oxide (K₂O) et al, and the optimal temperature of shells are 50 to 150℃ higher than that of limestone. The order of sulphation reaction for SO₂ is between 1 and 1.6, and the calcium sulphation ratio increases with the SO₂ and O₂ concentration when the O₂ concentration was less than 4.85%.A bench scale fluidized bed reactor was established for the experiments and a serious of desulphurization experiments of 5 kinds of sea shells were carried out on this reactor, as contrast, 1 kind of limestone was chosen also. As results, the desulphurization efficiency of shells are higher than that of limestone, and increase with Ca/S mole ratio and temperature in some range; the optimal temperature are little lower than that in TGA.Scan electronic microscope （SEM） and mercury porosimeter were used to measure the microstructure of some absorbents. Contrast to the limestone, the original shells has big pore diameter, big specific volume and big specific surface area; when they are calcined, the major range of pore diameter is between 0.2 and 5jim. While in the limestone, in despite of larger specific surface area, but the specific volume is very low, the pore diameter is only between 0.005 and 0.1 μm. Farther, within the shells, the high specific surface area corresponding to the high calcium sulphation ratio, so we can conclude that the reasonable pore size in absorbent for desulphurization may larger than 0.2 um and as small as possible on this base. With the temperature rise, the shell, which have big original pore size, have a decrease in pore size, while the limestone whose original pore size are small have an increase in pore size and a decrease in specific surface area, these lead to the decrease of reaction rate of sulphation. On the basis of the pore structure, the fractal dimension of the pore of absorbent was investigated. The results show that the shells have big fractal dimension but the limestone have small one respectively, and the absorbent, which have big fractal dimension, corresponding higher optimal sulphation temperature.A particle-pore size distribution model was made to describe the sulphation of the absorbent, which was on the basis of an un-reacted core model and a distributed pore sizemodel and the researching of the chemical reaction and the diffusion of reacted gases of the desulphurization. This model was coherent with the experimental results and being considered to used更多还原